Metallic debris detection sensors are known that use a magnetic sensor head and a hall-effect sensor, such as the hall-effect sensors sold under the trade name Micronas 815 or 855. The hall-effect sensor generates an error signal corresponding to the magnetic field at the probe. The sensor head is placed in a fluid medium, such as machine lubricant, and metallic debris is attracted from the fluid onto the magnetic sensor head. This accumulation of metallic debris on the magnetic head alters the effective magnetic field of the sensor head and thereby the error signal generated by the hall-effect sensor. The analogue error signal from the hall-effect sensor is digitized, typically using a 12-bit analogue to digital converter (ADC), then scaled and output as a signal indicative of the accumulation of debris. The digitized signal is input into a programmable integrated circuit (PIC). The PIC takes the digitized signal and converts it into a quantifiable amount of debris.
The signal produced by these prior art devices is responsive not only to debris on the sensor head but also to temperature. For use in certain situations, for example in a machine operating in a steady state and at constant speed, the operating temperature remains reasonably static and the known sensor operates satisfactorily. However, if the operation of the machinery results in thermal variations in the measured medium, then the output of the device is subject to variations due to the changes in operating temperature, which the device interprets as a change in debris accumulation, resulting in a drift or error in the output of the device.